In certain industries it is desirable to measure features or properties of a medium, such as properties of solids, liquids or gases (or combinations thereof). Such mediums may be provided in a container, pipeline, reservoir, conduit, or the like. An example of a medium might be a coolant in a cooling system conduit, or a flow of hydrocarbons in a transportation/production pipeline. In some instances, mediums can comprise two or more layers, each layer being a different density and/or different phase. Such mediums may be considered to be multi-layered.
An example of a multi-layered medium may be hydrocarbon gas and oil, provided in a pipeline, in which the gas and oil are provided as different layers due to the difference in their relative densities. In an alternative example of a multi-layered medium, a conduit comprising a deposited build-up of matter on the inner wall may be considered to be a first layer, while the material passing through the conduit may be considered to be a second layer of the multi-layer medium.
It can be desirable to make measurements to evaluate/estimate properties of mediums (multi-layered or otherwise), such as the flow rate, deposition thickness, etc. In order to do so, signals may be propagated into, or through, the medium (or multi-layered medium). To derive useful information from such signals, an accurate appreciation of the speed of such a signal in the medium, and in each layer, is looked-for (e.g. an accurate appreciate of the speed of an acoustic signal propagating in a layer or medium). Different signal species may be used depending upon the measurement. Signal species may include species such as acoustic signals, electromagnetic signals, optical signals, etc.
The speed of such signals species can be dependent on many factors. For example, the speed of an acoustic signal passing through a medium will vary depending on the density of that medium, which will vary depending upon the temperature of that medium. Similarly, varying refractive indices of a particular media will vary the speed of a propagating optical signal.
In many cases, the speed of a signal species in a medium is either guessed by having a prior knowledge of the medium in question, or is estimated or evaluated by using secondary information, such as temperature measurements and look-up tables (e.g. measuring the temperature and comparing this with known data for that particular medium at that temperature). In each case, making inaccurate presumptions about the medium in question can provide inaccurate results, and thus an inaccurate speed of a signal propagating in that medium is provided. The requirement to make various assumptions typically requires complex calculations to be performed which can significantly increase processing time, limiting the capabilities of existing techniques.
Such inaccurate measurement can often be provided in the oil and gas exploration and production industry, such as when monitoring the fluid flow in a multi-fluid/multi-layered pipeline, which can result in serious processing hazards, and/or an undesirable increase in operational costs.